In recent times, the use of asphalt-impregnated polyester sheet for roofing construction has been found to provide excellent results. The polyester sheeting is generally treated with asphalt and other water-resistant materials in the factory, because of the difficulties experienced with applying water-proofing materials to the polyester at the roof site. Untreated, non-woven polyester sheet does not generally withstand heat, and does not easily absorb hot asphalt.
Untreated, polyester sheet has been used with asphalt in cold-process roofing systems, wherein the asphalt is modified with latex or polypropylene and sprayed in a cold liquid state upon the polyester sheet. The cold process roofing systems have not been entirely satisfactory, because they tend to remain tacky for many months. This tackiness hinders the completion, repair and/or inspection of the roof, since the roof cannot be walked upon while tacky.
Even where hot asphalt systems have been contemplated with the use of polyester sheet, the asphalt generally requires torching on the roof, which is an unsafe, fire-hazardous procedure.
Therefore, most roofing applications using polyester materials have been with a polyestermat, i.e., a factory asphalt-impregnated polyester sheet.
The drawback of using factory impregnated polyester sheeting, however, is the high cost and inconvenience of shipping and handling these heavy rolls of material.
The present invention contemplates the construction of a roof using a polyester-hot asphalt or coal tar process at the roofing site, without the aforementioned disadvantages.
Hot, built-up roofing can now use plain, non-woven polyester sheet for the reasons that the polyester is now being manufactured with a resin treatment that assists the polyester to withstand the temperature (450 degrees F.) of hot asphalt and other hot-applied water-proofing ingredients.
In addition, torching the asphalt on the roof is no longer necessary with the advent of a new hot pumping system, wherein the asphalt is pumped in a hot fluid state to the roof.
The advantages of building-up a roof with hot water-proofing ingredients and polyester sheeting are many.
The rolls of plain, non-woven polyester sheet are light in weight and inexpensive to purchase and ship.
Plain polyester rolls are easier to work with, and a single, light-weight ply is often all that is required to produce an efficacious roof construction.
According to this invention, the polyester and asphalt layers can be melded together and simultaneously directly attached to the roof substrate as a composite membrane. This inventive method of forming and affixing a composite membrane simultaneously, in situ, not only reduces the costs of fabrications, but also provides a roof of better quality and adhesion.
The inventive method and construction will be explained in more detail, hereinafter.
The composite membrane technique of this invention can be used with different roof base sheets or substrates and overlays of foam, such as polyurethane and isocyanurate, to provide a roof composite construction of exceptional durability.
The polyester sheet is manufactured in a wide strip of approximately 162 inches in width. This strip is trimmed at each edge to provide a finished large strip of approximately 160 inches across. The large 160 inch strip is then cut into quarters to provide the standard forty inch strips common to the industry.
The forty inch roofing strip is a standard strip size used for the past 40 years. The reason the roofing strips were never cut larger, was probably the result that most strips of fiberglass, felt and pre-impregnated asphalt materials were too heavy to conveniently handle and ship in larger width sizes.
However, with the advent of the light-weight polyester sheet of this invention, came the idea that larger width sizes could be utilized in order to reduce the amount of loading and handling of the polyester rolls.
Also, the use of wider sheet reduces the amount of seams on the roof by one-third. The reduction of the number of seams is beneficial in two ways: (a) it reduces the amount of labor in applying the sheets in side-by-side fashion; and (b) it reduces the probability of leaks, because the seams are the weakest part of the roof construction.
In a recent experimental construction of a roof, it has been unexpectedly found, that another advantage is to be gained from the use of wider polyester stripping.
Polyester strips of approximately fifty-four (54) inches in width were used and found to drape more easily over the uneven surfaces of the roof substrate and/or base sheets, i.e. the wider polyester strips more closely conformed to the existing roof surface. This conformity has the advantage of providing a roof with a more level and even surface. Water run-off can be more carefully controlled, and puddling can be eliminated or reduced.
The reason that wider strips conform more closely is not known, but it is probably a result of the increase in flexure that the wider strip provides.
Another advantage of the wider width size, provides that only two cuts (3 strips) rather than three cuts (four strips) need be made in the 160 inch master sheet. This naturally will reduce manufacturing equipment and blade wear.
It is also contemplated that widths of weight (80) inches may be used, to further reduce labor and manufacturing costs.